Magnetic mercury



United States Patent 3,130,044 MAGNETIC IVERQURY Max H. Fiindt, 3531Emerson St, Palo Alto, Calif. No Drawing. Filed June 36, 1961, Ser. No.120,941 8 Claims. (Cl. 75169) This invention relates in general to aprocess for preparing and stabilizing a magnetically sensitive fluid andto the product.

it is an object of this invention to provide a process for thepreparation of a stable fluid which is sensitive to a magnetic field.

It is a further object of this invention to provide a fluid which issensitive to a magnetic field and which exhibits unusual stability.

Another object of this invention is to provide a magnetically sensitivefluid of low viscosity, i.e. a viscosity approaching that of puremercury.

Other objects and advantages of this invention, if not specifically setforth, will become apparent during the course of the description whichfollows:

It has been found that a superior mercury product which is sensitive toa magnetic field may be prepared by incorporating iron in mercury eitherby a chemical replacement reaction, utilizing a sodium or potassium andmercury amalgam, or by an electrolytic process using mercury as thecathode and that the product is stable,

especially after it has been washed with hydrochloric acid to remove thelargest iron crystals, provided that it is maintained in a system suchthat continued volatilization of mercury cannot occur. If volatilizationof mercury is permitted, as by storing or using the mercury in open airwith no protective film on the surface thereof, mercury is lost and theiron amalgamated therewith is released to form a black or brown coatingon the surface thereof and, in addition, a portion of the mercuryremaining loses its magnetic susceptibility.

A convenient method for preventing volatilization of mercury is toutilize it in a closed system which may contain a large gas-filled spacewhich is in equilibrium with respect to mercury vapor so that no furthermercury can be evaporated from the surface of the magnetically sensitivefluid. Pure mercury may be introduced into the system at the outset anda state of equilibrium established before introduction of themagnetically sensitive fluid or, in the alternative, a small amount ofanother liquid having a greater Vapor pressure than mercury may beintroduced into the system together with the mercury, such fluid beingpresent in suflicient quantity that equilibrium conditions will beestablished in the sstem before all of the added liquid has volatilized.

The product prepared chemically or electrolytically and so treated,especially if first shaken with concentrated HCl to dissolve anyabnormally large iron grains which may be present in the mercury, willbe stable for an indefinite time period.

In the chemical replacement reaction, sodium or potassium is firstincorporated in the mercury by direct union (preferably in the presenceof a small amount of water) and the sodium-mercury or potassium-mercuryamalgam is contacted with an iron salt which may be in the hydratedform, thus applying sufiicient water for the reaction) or may be in theform of a concentrated aqueous solution. In the electrolytic process,iron is electrolytically deposited from a dissociated iron salt insolution (FeCl R280 etc.) an iron or carbon rod conveniently serving asthe anode and the mercury serving as the cathode. The method describedin co-pending application Serial No. 80,736, filed January 5, 1961, nowabandoned, may also be used to form the amalgam, though this method isnot preferred since it results in a highly granular product of somewhatreduced stability.

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Preferably, the mercury is subjected to the electrolysis only for asufficient period of time to cause the mercury to exhibit enoughmagnetic susceptibility to be attracted to a small permanent magnetdipped into the mercury, such as a small horseshoe magnet having polepieces about A" in cross section. Removal of the magneticallysusceptible fraction immediately after rormation by immersing the magnetin the mercury yields a product of low viscosity and limits theformation of large iron crystals in the mercury which tend to growpreferentially, thus yielding a grainy product which deterioratesrapidly. Also, strong agitation of the mercury or a flowing actionduring the period that the current is passing is desirable since thisalso tends to limit the formation of the large iron crystals within themercury. A current density per square decimeter not in excess of 20 ampsis recommended with an EMF. not in excess of 6 volts. Lower currentdensities and voltages reduce the iron grain sizes.

Vigorous agitation of the mercury is desirable also where the chemicalreplacement reaction is utilized or the process described in theaforementioned co-pending patent application is used, such agitationtending to reduce the grain size and increase the stability of theproduct.

The appearance of the product is improved considerably and a bright,silvery-appearing product lacking black or brown iron deposits isassured if the product is agitated with concentrated or dilute HCl afterit is removed from the reaction vessel.

Whether the product is so washed with HCl or not, it is absolutelyessential that it then be stored in a closed system wherein litle or nomercury is permitted to evaporate. As mercury evaporates, iron isreleased from the amalgam and oxidizes, appearing on the surface of thefluid product in the form of a black or reddish-brown powder or scum. Afurther important effect of permitting volatilization of the mercuryover any extended period of time is that the entire sample tends to loseits magnetic susceptibility. After several days in the open air, asample which is initially entirely magnetically susceptible will befound to be less than one-half magnetically susceptible with theremainder of the mercury in the vessel being completely insensitive tothe presence of a magnet. As noted earlier, there are several methodsfor preventing such volatilization of the mercury, the preferred beingthe use of a non-oxidizing fluid which is inert to mercury and iron as acover liquid. Thus, even if the system is heated, the second fluid willvaporize more readily than the mercury, quickly establishing a state ofequilibrium in the system and preventing further vaporization of themercury. Preferred cover liquids are concentrated HCl or H PO' aqueoussolutions of HCl, H 50 H BO H PO or H CO concentrated solutions ofalkali metal or alkaline earth metal salts (especially the halides) orhydroxides; the various borate esters and anhydrides, both aliphatic andaromatic, and salts thereof, in an aqueous solution if necessary;alcohols; vegetable oils and mineral oils; as well as any of thecommerical anti-oxidants of which examples are Shell Ionel and variousof the amines; and various buffer solutions such as an 0.1 N solution ofphosphoric, phenylacetic and boric acids, for use where a non-corrosivecover liquid is required.

In addition to utilizing a small amount of the fluid or a sealed,gas-filled vessel as means of preventing volatilization of mercury,deposit of iron on the surface thereof, and rusting of the iron, it isalso possible to use a sealed vessel containing an inert gas such asargon or nitrogen. If the gas is present in sufiicient quantity at theoutset, little if any volatilization of mercury will result and, in anycase, any iron deposited out of the mercury will not oxidize. This,however, is a less preferred embodiment of the invention since a fluidacts as a lubricant for the mercury in the system and since various ofthe cover liquids named (especially concentrated HCl) act to reduce theviscosity of magnetically susceptible mercury with which they are incontact.

Another important feature of this invention is the incorporation of atleast one of the metals bismuth, aluminum, chromium, magnesium,antimony, cadmium, tin, or titanium in the amalgam of iron and mercury.Bismuth, magnesium and aluminum have a dramatic effect upon theviscosity and magnetic susceptibility of the mercury-iron amalgam and onthe stability thereof. Antimony, cadmium, tin and titanium so affect theamalgam also, but to a significantly lesser degree, the first three ofthese metals yielding a product which wets glass.

These metals may also be used in admixture with one another or othermetals than those listed may be added. Bismuth and tin mixtures, bismuthand aluminum mixtures, and bismuth, tin and lead mixtures have all beenadded to mercury-iron amalgams. Such metals as cobalt, nickel, and zincmay also be added to the mercury; however, nickel, cobalt, lead, andZinc do not beneficially affect the viscosity of the mercury. It isdesired that between 90% and 98% by weight of the product constitutemercury, with the remainder constituting the iron, where a two-componentamalgam is prepared. However, where an additional metal is added, as inthe preferred embodiment of this invention, the mercury may constitutebetween 50% and 96% by weight, with 2% to 40% representing the thirdmetal(s) and the remaining 2% to 10% representing the iron. A preferredproduct contains, by weight, 65-93% mercury, 2l0% iron, and 5-25%bismuth, magnesium, aluminum, chromium, or antimony.

Examples are set forth below for illustrative purposes but these are notto be construed as imposing limitations on the scope of the inventionother than as set forth in the appended claims.

Example 1 A quantity of 7.3 grams mercury was placed in an electrolyticcell containing a saturated aqueous solution of ferrous chloride. Aninsulated copper wire was immersed in the cell with the bottom A" leftbare and completely immersed in the mercury. Six volts D.C. wereimpressed upon a soft low-carbon iron anode (a nail), this anode restingin the cell in such a manner that it did not contact the mercury. Thecurrent density was amps/square decimeter and the aqueous solutiontemperature was about 90120 F. After ten minutes, during which time themercury became somewhat more viscous, a portion of the mercury wasremoved from the cell with a small Alnico V magnet, washed twice bybeing vigorously agitated with several volumes of tap water, and driedwith soft, adsorbent paper. This product was divided into two fractions,both of which were shaken with distilled Water over a three-day period.One portion was then allowed to stand under distilled water while thesecond portion was placed in the test tube under /2 gram soluble oil.Both samples remained shiny, sensitive to magnetic fields, and showed nosigns of deterioration when stored in the open test tube for an extendedperiod of time.

Example 2 About 3.3 grams mercury was placed in the cell containing aconcentrated lithium chloride electrolyte and provided with the sameiron anode and current source described in'Example 1. After a period ofabout ten minutes, during which time bubbles were evolved at thecathode, the lithium chloride was removed and replaced with ferrouschloride in saturated aqueous solution. Current was impressed on theanode for an additional. ten minutes, and the product became noticeablymore viscous. A portion of the mercury was removed from the cell,washed, and quickly dried and placed in a test tube under a layer ofThree-in-One oil, where the product was stored without detectabledeterioration. A portion of this product was stored in the absence ofadded oil and in the open air, and it was found that the lithium in themercury attracted moisture, forming lithium hydroxide in water solution.

Example 3 A quantity of 5 grams mercury was placed in a vesselcontaining stainless steel which had been dissolved in concentrated 20B. hydrochloric acid. The mercury lay at the bottom of the cell and aninsulated copper wire was placed in the cell with the bottom A left bareand completely immersed in the mercury. A stainless steel rod was usedas the anode and it was placed in the cell in such a manner that it didnot contact the mercury but merely dipped into the ferrous chloridesolution so formed. A six volt automobile battery was connected to theanode and current supplied for a period of about ten minutes. Themagnetically susceptible fraction was shaken with a saturated aqueoussolution of CaCl and dried. The magnetic fraction was divided into twoaliquot portions, and one was placed under a layer of a saturatedsolution of calcium chloride and the other was covered with solid(powdered) calcium chloride which, because of its deliquescentproperties, subsequently formed an aqueous solution. Both samplesmaintained their susceptibility to magnetic fields. However, theappearance of the product deteriorated somewhat, sufiicient free ironmaterial being formed over two weeks time t cause the cover liquid toturn reddish-black. In additional runs where theproduct was washedimmediately after preparation with concentrated (20 B) HCl, thisdeterioration in appearance was not encountered.

Example 4 A small piece of copper-containing Alnico magnet (Alnico V)was crushed and dissolved in concentrated hydrochloric acid to yieldabout 3 cc. of solution. Utilizing an anode consisting of another pieceof Alnico V magnet, a mercury product was obtained electrolytically (asin Example 3) incorporating the Alnico magnet material. The magneticallysusceptible portion of the product was washed and dried and a saturatedaqueous solution of CaCl in a quantity volumetrically equivalent to thatof the mercury product was added and the mercury stored for an extendedperiod of time without apparent deterioration in appearance or insusceptibility to a magnetic field. Example 5 Example 6 An electrolytewas prepared by pouring concentrated HCl over nails and the solutionwhich formed after the reaction had been completed was decanted; 5 gramsof mercury cathode contained in a glass jar was agitated by dipping asteel rod into it at 3 cps. Using a lowcarbon iron nail as an anode, aproduct weighing about 5.2 grams was prepared which was washed anddried. The product was smooth, mobile and magnetically susceptible andwas stored open to the air in contact with powdered CaCI whicheventually formed an aqueous solution due to exposure to moist air. Theproduct maintained its magnetic susceptibility throughout the storageperiod, but the appearance deteriorated somewhat, a small amount ofblack powder clouding the CaCl solution after about two weeks time.

Example 7 A quantity of 8 grams of mercury and 0.1 gram sodium formed anamalgam, the sodium being cut into small pieces 0A and impressed beneaththe surface of the mercury piece by piece. A grinding action resulted ina reaction, sparks, and vaporization of mercury. The mercury becameprogressively more viscous as the sodium was added. A large excess ofFeCl -4H O was added to the reaction vessel and the entirety vigorouslyagitated with a stirring rod, the hydrated ferrous chloride providingmost of the water for the exchange reaction, with a few drops ofadditional water being added. There was a vigorous exothermic reaction.Following washing, the product was found to be magnetically susceptibleand capable of supporting itself when it was placed tightly against apiece of paper surrounding a pole piece of a small permanent magnet. Thesample was divided into two parts, one of which was treated with anadditional .1 gram sodium, resulting in the formation of a solidamalgam. To this was added a saturated solution of SnCI A reactionensued and the product was washed with 2 N HCl, followed by water, andstored under a layer of 2 N HCl without any apparent deteriorationeither in magnetic susceptibility or appearance. The resultant producthad a somewhat lower viscosity than the iron and mercury amalgamprepared initially. The second portion of the iron-mercury amalgam wassimply shaken with stannous chloride solution, no sodium having beenadded thereto. There was no effect on the viscosity or appearance of theproduct and it was apparent that none of the tin had found its way intothe malgam. Similar results were obtained when a chromous chloridesolution was contacted with a sodium-iron-mercury amalgam, on the onehand, and an iron-mercury amalgam on the other. Further, the sampleshaving no tin or chromium therein showed considerably less stabilitythan the products into which tin and chromium had been incorporated bythe sodium replacement reaction.

Example 8 A quantity of 165 grams of mercury and 2.2 grams sodium weretriturated together to form an amalgam and the amalgam allowed to standovernight. T o the resultant amalgam was added an excess of FeCl -4H Ocrystals and a few drops of water to initiate a reaction. A dark greenviscous mass formed and hydrogen evolution was apparent; at one point,it burst into flame. On cessation of the exothermic reaction, theproduct was washed and dried and to it was added an additional 2.2 gramssodium which was ground beneath the surface of the mercury, a similarviolent reaction ensuing, and an amalgam containing quantities of solidsbeing formed. An excess of crystalline FeCl -4H O was added togetherwith several drops of water and again there was a strong exo thermicreaction. Sufficient metallic sodium was added to form a solid amalgamand the entire mass was divided into a series of samples:

(a) To a first portion was added an excess of stannous chloride crystalstogether with a drop of water. A gray fluid formed. The product waswashed with water and then concentrated HCl, being shaken therewith sixtimes over three days. No further deposition of iron occurred and theproduct exhibited excellent magnetic susceptibility and was onlyslightly duller in color than pure mercury. Also, its viscosity was onlyslightly greater than that of pure mercury. It was stored with severaldrops of concentrated (20 Be'.) HCl in a closed bottle and showed notendency to deteriorate, either in appearance, magnetic susceptibility,or viscosity over a period of several weeks.

(b) To a second portion of the sample was added an excess of MgCl -6H Ocrystals. A mildly exothermic reaction ensued. After six washings overthree days with concentrated (20 Be.) I-lCl, the product was storedunder the HCl in a capped vial. A point of stability had been reachedafter the aforementioned several washings with concentrated HCl and aproduct exhibiting a viscosity approaching that of pure mercury, a veryshiny appearance, and high magnetic susceptibility, was obtained.

(0) To a third portion of the sample was added CrCl -6H O crystals inexcess; a strongly exothermic reaction ensued and a dark green solutionformed. The product was shaken with HCl six times over a period of threedays, a small amount of HCl added and the product placed in a sealedvial. No deterioration in appearance, magnetic susceptibility orviscosity was apparent over several weeks.

(d) To a fourth portion of the sample was added AlCl -6H O crystals inexcess; a mild reaction ensued with a gray precipitate being formed. Theproduct was shaken with 20 Be. HCl six times over three days and the HClwash was replaced with a few drops of fresh HCl (a sufiicient quantityto form small droplets on the surface of the mercury). As in the othertests aforementioned, the top was placed on the bottle so that themercury could not volatilize. The viscosity of the product approachedthat of pure mercury and no precipitation of ferrous or ferric oxidesappeared on the surface over several Weeks. The magnetic susceptibilityof the product also appeared to be unchanged following theaforementioned storage period.

(e) To a fifth portion of the sample was added CdCl -2 /zH O crystals inexcess. A strong exothermic reaction ensued, with a gray precipitateforming. The product was treated with HCl as in (d) above, a productbeing obtained which wetted glass slightly and was unusually bright andshiny, but exhibited somewhat less magnetic susceptibility than thealuminum, chromium, and magnesium samples described above. Its magneticsusceptibility was about that of the sample containing tin.

(f) Antimony metal was filed into small particles and treated with 20 B.HCl to form a solution thereof. This was then added to a sixth portionof the aforementioned ironand sodium-containing amalgam and a re actionensued yielding hydrogen. The product felt somewhat granular, asparticles of the antimony had found their way into the amalgam inaddition to the antimony which was dissolved in the l-ICl. The solidparticles tended to appear at the surface of the amalgam in time andeventually a smooth antimony-containing amalgam was secured. The amalgamwas washed with Water and shaken six times with 20 B. HCl over the nextthree days and then stored in a closed bottle in contact with a smallamount of concentrated HCl. There was no further noticeabledeterioration. The product exhibited excellent magnetic susceptibility,its appearance closely resembling pure mercury, and a very low viscositywhich also approached that of pure mercury.

(g) To a seventh portion of the aforementioned batch ofmercury-iron-sodium amalgam was added an excess of Bi(NO '5H O crystalsand a drop of water to initiate the reaction. Quantities of red nitrousoxide gas were evolved. The product was washed with water and shaken sixtimes with the concentrated HCl over the next three days. The productwas then stored in a closed bottle in the presence of only sufficientconcentrated HCl to wet the surface of the product. The viscosity ofthis material was the lowest of all samples reported above, theviscosity very closely approaching that of pure mercury. This samplealso remained bright and shiny, closely resembling pure mercury, andexhibited very high magnetic susceptibility. This bismuth-containingproduct was superior to the others described above in magneticsusceptibility and mobility.

A portion of the sample discussed in sub-section (g) above was separatedfrom the main portion of the sample after the three days washing withHCl had been completed. This material was in turn separated into twoaliquot portions and these stored in sealed vessels in an 7 atmosphereof argon and nitrogen, respectively. The total volume of each bottle wasabout three times that of the mercury therein. No deterioration in thesamples after three weeks storage was apparent. Each remained shiny,mobile, and magnetically susceptible.

(h) To an eighth portion of the batch was added an excess of liquid TiClA strong reaction ensued; the mercury product was washed with water,shaken six times over three days with 20 B. HCl, and stored in a closedbottle in contact with the HCl, as previously described. The productexhibited good stability and fair mobility and magnetic susceptibility.

(i) The last portion was treated, as aforementioned, with water toremove the sodium, no additional metal being added. The product waswashed with additional water and concentrated HCl as were the productsabove and stored in a closed bottle under enough of the aforementionedHCl to slightly wet the product surface. The product exhibited excellentstability, but its magnetic susceptibility was lower than the bismuth,aluminum, magnesium, and chromium samples described above and about thesame as the magnetic susceptibility of the tin and cadmium samples,though the viscosity of the sample containing no additional metal Wassomewhat higher than either of the last two mentioned as well as of theothers.

When any of the aforementioned products were left uncapped for asufiicient period of time for the small amount of acid in the bottle toevaporate, a black powder (ferrous oxide) or a rust (ferric oxide) beganto form on the surface. To prevent the deterioration of the product;therefore, it is important that it be stored either under a layer of asuitable fluid or that the vessel containing the product be sealed so asto prevent the loss of mercury through volatilization. Preferably, bothprecautions should be taken.

In various additional tests, amalgams containing mixtures of metals inaddition to mercury, iron and one of the preferred additive metalsmentioned above were prepared by the sodium replacement reaction usingthe chlorides of the metals incorporated. For example, an amalgamcontaining both tin and lead was formed; an amalgam containing bothbismuth and cobalt was formed; and an amalgam containing cobalt andaluminum was formed.

Example 9 A quantity of 16 grams of mercury was placed under anapproximately 1 inch saturated solution of ferrous chloride in a largetest tube. A soft iron nail was used as the anode and a six volt batteryconnected thereto with a wire, insulated to a point beneath the surfaceof the mercury, dipped thereinto to provide a cathode. The current wasallowed to flow for approximately minutes, throughout which time themercury and ferrous chloride were vigorously agitated. The entire 16grams became somewhat more viscous and was attracted to a magnet. Theferrous chloride was then drained off and aluminum chloride in the formof a super-saturated solution of about height was substituted. Analuminum anode was used and the current permitted to flow for about 5minutes during which time the solution boiled. Thereafter, 8 grams ofmercury w hich adhered to a magnet was withdrawn. Two aliquot portionswere vigorously agitated a saturated calcium chloride solution on theone hand and concentrated (20 B.) HCl on the other; each was placedunder a layer of the same liquid and shaken therewith daily for threedays. This assisted in the removal of the largest grains of iron withinthe amalgam. The cover liquid, in the case of the calcium chloride,formed a faint green color immediately after being added 'to themercury, indicating the formation of ferrous chloride. After the threeday period, the cover liquids were decanted and the 02101 solutionreplaced. The sample treated with H01 was divided into three portions,one of which was again placed under concentrated HCl, one under 1 N HCland another in a dry vial having twice the volume of the mercury. Thesamples all exhibited viscosities approaching that of pure mercury andwere stored in sealed vessels for four Weeks without any apparentdeterioration, except [for the sample lacking a cover liquid, whichsample became slightly reddish on the surface thereof. Thisdeterioration in appearance did not continue after the first few daysand the sample remained mobile and magnetically susceptible throughoutthe storage period. All had a magnetic susceptibility substantiallysuperior to that of pure mercury-iron amalgam prepared without theaddition of the aluminum.

Example 10 An amalgam consisting of about 7 grams of mercury and about 1gram of iron, prepared electrolytically, was treated to incorporatecadmium from a cadmium chloride solution using an iron nail for theanode and a six volt D.C. battery over a period of about 10 minutes. Thecircuit resistance was about .8 ohm. The product wetted glass, thusindicating that cadmium had gone into the mercury. The viscosity of theproduct was somewhat less than that of an amalgam containing no metalother than iron and mercury. The product was stored in a bottle of abouttwenty times the volume of the mercury and sufiicient saturated CaClsolution was added to just wet the mercury surface. No deterioration wasapparent after three weeks.

Example 11 An additional electrolytic run was made utilizing a saturatedsolution of stannous chloride and a product was obtained which was alsostored under a saturated solution of calcium chloride.

Example 12 A dish was filled to about a one inch depth with mercury,providing a surface area of about 12 square inches and current passedfrom the aforementioned six volt battery into a saturated ferrouschloride solution which had been poured over the mercury to a depth ofabout three inches. A small Alnico horseshoe magnet'having about A polepieces was dipped into the mercury as the cur rent flowed and themagnetically susceptible fraction removed. About 25 grams were collectedand divided into a series of samples. All were shaken vigorously withconcentrated HCl four times over two days and then placed under aboutMr" of various cover liquids. The samples placed under a saturatedaqueous solution of boric acid; ethyl alcohol; light machine oil;saturated aqueous solutions of CaCl MgCl NH Cl and NaOH; olive oil; 3 NHCl; 2 'N HCl; 1 N HCl; 20 B. H01; 1 N H concentrated H PO Shell lonel;distilled water; and pyridine remained shiny, magnetically susceptible,and of low viscosity throughout the test period. The samples under the HPO and 20 B. HCl'ap'peared superior in that their viscosities remainedlowest of any of the samples. Samples oat the mercury product placedunder concentrated HNO CCl kerosene, acetone and N aI-IClO rusted withinseveral days, as the cover liquids either attacked the mercury orpromoted oxidation of the iron component.

When one of the aforementioned metals Bi, Cr, A1, Mg, Sb, Cd, Sn, and Tiis added to an amalgam containing mercury and iron, unusual stability iscontributed to the product. These magnetic mercury products, in additionto having the improved viscosity characteristics, magneticsusceptibility, etc. described above, may also be used out of a sealedvessel for extended periods of time (especially at temperatures of lessthan 30 C.) without there occurring suflicient volatilization of themercury to result in an iron material appearing on the surface as acontaminant. However, it is preferred to maintain all magnetic mercuryproducts in sealed vessels except when it is necessary that they beexposed to open air temporarily, since mercury has relatively high vaporpressure and will volatilize, thus freeing a certain amount of the iron.

The additional metals just mentioned may also be incorporated in themercury through electrolytic means. All except bismuth may beelectrolyzed from their chloride or other salt solutions underconditions similar to those described above as applied to ferrouschloride.

Bismuth may be electrolyzed from an aqueous solution of Bi(NO in diluteHNOg or from an aqueous solution of Bi O and H010 In any case, theconditions recommended for plating these various elements onto solidsurfaces are satisfactory as applied to incorporating them into mercury.

As aforementioned, the use of one of the aforementioned or a similarnon-oridizing fluid which is inert to mercury and iron (though possiblya solvent therefor, to some extent) reduces or completely eliminates thedeterioration of the amalgam, almost or completely preventing theformation of a scum of black powder or reddish-brown material on thesurface thereof. The product exhibiting the best appearance andstability is obtained where both a sealed vessel and a small amount(sulficient to wet the mercury surface after equilibrium is reached) ofrelatively concentrated HCl is placed within the vessel in contact withthe mercury. Only enough to provide most of the vapor molecules to fillthe system is required and this may even be insufiicient entirely tocover the surface of the amalgam if low temperatures (room temperature)of use are contemplated. Larger quantities are required at highertemperatures where there is a greater opportunity for volatilization ofmercury and release of the iron component.

in addition to use in magnetic clutches, the magnetic fluid of thisinvention finds particular utility in mercury switches which need not betilted or have any moving parts excepting the mercury contained within.The contacts enter the chamber partially filled with the mercury at somepoint near the top thereof, which point is adjacent an electromagnet.When the magnet is energized, the mercury bridges the gap between thecontacts, permitting the circuit to be completed.

Application Serial No. 80,737, filed January 5, 1961, describes asimilar product prepared by adding iron filings to a mercury-sodiumamalgam. The product of this co-pending application may also bebeneficially affected with respect to stability when stored as describedand claimed herein.

Obviously, many modifications and variations may be made withoutdeparting from the spirit and scope of this invention, and thereforeonly such limitations should be imposed as are indicated in the appendedclaims.

This is a continuation-in-part of application Serial No. 80,737, filedJanuary 5, 1961, now abandoned.

I claim:

1. A fluid sensitive to a magnetic field consisting essentially of anamalgam of between about 2 and 40 weight percent of a metal selectedfrom the group consisting of bismuth, aluminum, chromium, magnesium,antimony, cadmium, tin and titanium and between about 2 and 10 weightpercent iron, with the remainder being mercury.

2. A fiuid sensitive to a magnetic field consisting essentially of anamalgam of between about 2 and 40 weight percent bismuth and betweenabout 2 and 10 weight percent iron, with the remainder being mercury.

3. A fluid sensitive to a magnetic field consisting essentially of anamalgam of between about 2 and 40 weight percent magnesium and betweenabout 2 and 10 weight percent iron, with the remainder being mercury.

4. A fluid sensitive to a magnetic field consisting essentially of anamalgam of between about 2 and 40 weight percent aluminum and betweenabout 2 and 10 weight percent iron, with the remainder being mercury.

5. A fluid sensitive to a magnetic field consisting essentially of anamalgam of between about 2 and 40 weight percent chromium and between 2and 10 weight percent iron, with the remainder being mercury.

6. A fluid sensitive to a magnetic field consisting essentially of anamalgam of between about 2 and 40 weight percent tin and between about 2and 10 weight percent iron, with the remainder being mercury.

7. A process for preparing a fluid sensitive to a magnetic fieldconsisting essentially of forming a sodiummercury amalgam; contactingsaid amalgam with an ironcontaining material and permitting a reactionto ensue whereby to replace said sodium of said amalgam with the saidiron; and amalgamating therewith a third metal selected from the groupconsisting of bismuth, aluminum, chromium, magnesium, antimony, cadmium,tin and titanium whereby to form a product containing between about 2and 40 weight percent of the said third metal, and between about 2 and10 Weight percent iron, with the remainder being mercury.

8. A process for preparing a fluid sensitive to a magnetic fieldconsisting essentially of depositing by electrolysis iron into mercuryutilizing iron as the anode and said mercury as the cathode; andamalgamating a third metal therewith selected from the group consistingof bismuth, aluminum, chromium, magnesium, antimony, cadmium, tin andtitanium whereby to form a product containing between 2 and 40 weightpercent of the said third metal, and between about 2 and 10 weightpercent iron, with the remainder being mercury.

References Cited in the file of this patent UNITED STATES PATENTS2,089,731 Charlton Aug. 10, 1937 2,239,144 Dean et a1 Apr. 22, 19412,974,104 Paine et al. Mar. 7, 1961 2,983,349 Meiklejohn May 9, 1961

1. A FLUID SENSITIVE TO A MAGNETIC FIELD OCNSISTING ESSENTIALLY OF ANAMALGAM OF BETWEEN ABOUT 2 AND 40 WEIGHT PERCENT OF A METAL SELECTEDFROM THE GROUP CONSISTING OF BISMUTH, ALUMINUM, CHLROMIUM, MAGNESIUM,ANTIMONY, CADMIUM, TIN AND TITANIUM AND BETWEEN ABOUT 2 AND 10 WEIGHTPERCENT IRON, WIHT THE REMAINDER BEING MERCURY.
 7. A PROCESS FORPREPARING A FLUID SENSITIE TO A MAGNETIC FIELD CONSISTING ESSENTIALLY OFFROMING A SODIUMMERCURY AMALGAM; CONTACTING SAID AMALGAM WITH ANIRONCONTAINING MATERIAL AND PERMITTING A REACTION TO ENSUE WHEREBY TOREPLACE SAID SODIUM OF SAID AMALGAM WITH THE SAID IRON; AND AMALGAMATINGTHEREWITH A THIRD METAL SELECTED FROM THE GROUP CONSISTING OF BISMUTH,ALUMINUM, CHROMIUM, MAGNESIUM, ANTIMONY, CADMIUM, TIN AND TITANIUMWHEREBY TO FORM A PRODUCT CONTAINING BETWEEN ABOUT 2 AND 40 WEIGHTPERCENT OF THE SAID THIRD METAL, AND BETWEEN ABOUT 2 AND 10 WEIGHTPERCENT IRON, WITH THE REMAINDER BEING MERCURY.